The ability to match therapeutic compounds with cancer cells containing specific molecular aberrations can lead to profound and personalized anticancer activity. We have identified a class of compounds, exemplified by founding member PAC-1, which activate the enzyme procaspase-3, leading to apoptotic death even in cancer cells with common defects in their apoptotic cascade (e.g., p53 mutation, Bcl-2 overexpression, caspase-9 mutation). As many cancers overexpress procaspase-3, such procaspase-3 activating compounds have potential to be highly specific for cancer cells. As part of R01-CA120439, we elucidated the mode of action of PAC-1 in vitro and in cancer cells in culture, and explored its efficacy in advanced mammalian tumor models. Excitingly, in addition to its considerable single-agent efficacy, we have discovered that PAC-1 powerfully synergizes with standard-of-care drugs used in the treatment of two deadly cancers, glioblastoma multiforme (GBM) and metastatic osteosarcoma (OS), both of which express elevated levels of procaspase-3. In this renewal we will synthesize improved versions of PAC-1, assess them in sophisticated animal models of GBM and metastatic OS both alone and in conjunction with frontline therapies, and fully define the potential of PAC-1 to synergize with a variety of anticancer agents. Innovative aspects of this proposal include procaspase-3 activation as an anticancer target, the mechanistically-driven use of PAC-1 in synergy with conventional anticancer drugs, the exploitation of the blood-brain barrier penetrating property of PAC-1 for treatment of GBM, and the evaluation of PAC-1 in pet dogs with cancer, a highly relevant translational model and an opportunity to help these animals that might otherwise be euthanized. Our data suggest that PAC-1, both alone and operating in synergy with a wide variety of antitumor agents, has broad anticancer applications.